Electromagnetic navigation system for microscopic surgery

Abstract

The present invention relates to an electromagnetic navigation system for microscopic surgery and a method for microscopic surgery using said system. The present disclosure provides an electromagnetic navigation system for microscopic surgery, comprising at least a microscope and an electromagnetic measurement system comprising a field generator, wherein the field generator is fixed or adjustably connected to the microscope, and an additional disturbance correction module for compensating disturbances of the electromagnetic measurement system caused by the microscope.

Claims

1. An electromagnetic navigation system for microscopic surgery, comprising at least a. a microscope; and b. an electromagnetic measurement system comprising a field generator, wherein the field generator is fixed or adjustably connected to the microscope, and c. a physical shielding between surgical microscope and field generator wherein the shielding is fixed to the microscope and the field generator; and d. at least one sensor element with sensor coils for measuring the pose of navigated instruments and/or the patient; and e. a disturbance correction module for compensating effects of disturbances of the electromagnetic field caused by the microscope.

2. The electromagnetic navigation system of claim 1, wherein the field generator is arranged at the bottom of the microscope so that the electromagnetic measurement system tracks sensor elements in or near the field of view of the microscope.

3. The electromagnetic navigation system of claim 1, wherein the field generator is connected by an adjustment element to the microscope for optimizing intra-operatively the orientation of the generator relative to the microscope.

4. canceled

5. canceled

6. canceled

7. The electromagnetic navigation system of claim 1, wherein the sensor element is a patient tracker or pointer.

8. The electromagnetic navigation system of claim 1, further comprising a data acquisition unit for receiving the current microscope images, microscope settings and the current navigation data.

9. The electromagnetic navigation system of claim 1, further comprising a data storage unit in which a three-dimensional image data set of the object area containing the object volume is storable.

10. The electromagnetic navigation system of claim 1, further comprising a data processing unit with; (1). an image data registering module with which the pose of the three-dimensional image data set relative to the field generator can be determined; (2). a microscope registration module with which the intrinsic imaging properties and the pose of the microscope optics can be determined relative to the field generator for various zoom and focus settings of the microscope and, if applicable, for the current state of the adjustment element, based on a previous calibration or constructive parameters of the microscope; and (3). an image computation module for generation at least one of the following views/image data, with i. virtual two-dimensional image data with the positionally correct overlay of planning data in the microscope image and/or for image injection into the microscope optics ii. Slice images of the three-dimensional image data with optionally visualized planning data.

11. The electromagnetic navigation system of claim 1, further comprising an image display unit with which computed image data or views can be displayed.

12. canceled

13. A method for correction of navigation data during microscopic surgery using an electromagnetic navigation system, comprising the steps of; a. calibrating an electromagnetic measurement system for determining a mapping rule for the calculation of corrected poses of sensor elements to compensate for the effects of the disturbance of the electromagnetic field by the microscope and/or the shielding based on pose data of the sensor elements in a disturbance-free environment and based on zoom and/or focus setting of the microscore; and based on the change of the zoom and/or focus setting of the microscore; and b. use of a mapping rule to correct the poses data of the sensor elements during surgery.

14. The method of claim 13, wherein the mapping rule uses distortion mapping, wherein polynomials or splines are used for calculating corrected poses of the sensor elements.

15. The method of claim 13, wherein electromagnetic sensors are rigidly coupled to the microscope to detect changes of the electromagnetic field relative to the state of calibration.

16. canceled

17. canceled

18. The electromagnetic navigation system of claim 1, wherein the shielding has an opening at the position of the microscope lens in order not to interrupt the view of the microscope on the operation field.

19. The method of claim 10, wherein the electromagnetic navigation system for microscopic surgery comprise an adjustment element for adjustment intra-operatively the orientation of the field generator relative to the microscope and the mapping rule also bases on the setting of the adjustment element.

20. A method of use in microscopic surgery of an electromagnetic navigation system comprising at least a microscope and an electromagnetic measurement system comprising a field generator wherein the field generator is fixed or adjustably connected to the microscope, a physical shielding between the surgical microscope and the field generator wherein the shielding is fixed to the microscope and the field generator, at least one sensor element with sensor coils for measuring the pose of navigated instruments and/or the patient; and a disturbance correction module for compensating effects of disturbances of the electromagnetic field caused by the microscope, comprising the steps of: generating an electromagnetic field with said field generator; measuring a pose of navigated instruments or a patient using said sensor; and compensating for effects of disturbances of the generated electromagnetic field caused by the microscope and the shielding.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0038] The present invention will be described by figures and examples. It is obvious for a person ordinary skilled in the art that the scope of the invention is not limited to the disclosed embodiments. It shows:

[0039] FIG. 1 System setup with microscope and electromagnetic measuring system

[0040] FIG. 2 Possible embodiment of the field generator and its fixed mounting with shielding on the microscope, the field generator is arranged in a ring around the microscope lens.

[0041] FIG. 3 Further possible embodiment of the field generator and its adjustable mounting with shielding on the microscope

[0042] FIG. 4 Embodiment of FIG. 3 with indicated visual field of the microscope and measuring range of electromagnetic measurement system

[0043] FIG. 5 Data flow between the system components

DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention provides an electromagnetic navigation system for microscopic surgery, comprising at least a microscope; and an electromagnetic measurement system comprising a field generator, wherein the field generator is fixed or adjustably connected to the microscope, and a sensor with one or more sensor coils; and an additional disturbance correction module for compensating disturbances of the electromagnetic measurement system caused by the microscope

[0045] The terms ‘shield’ or ‘shielding’ will be used synonymously within the meaning of the present disclosure. The position and spatial orientation of a sensor for instance will be designated as the ‘pose’ of the respective sensor, so that pose summarizes position and spatial orientation within the meaning of the present disclosure. A ‘sensor element’ summarizes all elements bearing at least one sensor coil so that the pose of the sensor element within the electromagnetic field can be determined. A sensor element can be integrated into a pointer instrument, into a patient tracker or into any other element which might be used during surgery and wherein it is necessary to know the correct position of such a sensor element.

[0046] The following components may be part of the system: [0047] Surgical microscope with optional video output interface, with an optional image injection unit and an optional settings communication interface; [0048] Electromagnetic measurement system, consisting of a field generator, patient trackers and instruments, characterized in that the field generator is fixed or adjustably connected by an adjustment element to the operating microscope, and characterized by an additional disturbance correction module; [0049] Data acquisition unit for receiving the current navigation data and optionally the current microscope images and microscope settings as well as the state of the adjustment element; [0050] Data storage unit in which a three-dimensional image data set of the object area containing the object volume is storable; [0051] Data processing unit with: [0052] an image data registering module with which the pose of the three-dimensional image data set relative to the field generator can be determined [0053] a microscope registration module with which the intrinsic imaging properties and the pose of the microscope optics can be determined relative to the field generator for various zoom and focus settings of the microscope, if applicable, based on a previous calibration or constructive parameters of the microscope [0054] Image computation module for generation of the following views/image data: [0055] Virtual two-dimensional image data with the positionally correct overlay of planning data in the microscope image and/or for image injection into the microscope optics [0056] Slice images of the three-dimensional image data with optionally visualized planning data [0057] Image display unit for displaying computed image data or views [0058] optional: Physical shielding between surgical microscope and field generator, fixed to microscope and/or field generator

[0059] A surgical microscope is predominantly used in minimally invasive surgery and microsurgery. It is mounted on a floor or a ceiling support and is positioned and oriented above the patient by the surgeon. The microscope provides a magnified stereoscopic view of the operating field. The surgeon sees the image, which is captured by the microscope lens, through the two eyepieces of the microscope. The microscope image, perceived by the surgeon, is additionally optionally captured with the aid of photo sensors and provided via digital or analog video interfaces.

[0060] Some surgical microscopes have additional data interfaces for the exchanging the current microscope settings such as zoom or focus. Additionally, the possibility to include additional image data in the microscopic optics using beam splitters may be given (so-called image injection).

[0061] An electromagnetic measuring system consists of a field generator in which a number of coils are installed in different orientations. These coils generate an alternating electromagnetic field. Further components are one or more small sensor coils located within the sensor, in which a current is induced by the electromagnetic field. By measuring the induced current, the measurement system can uniquely determine the position of the sensor coil, respectively the sensor. These coils are used as part of patient trackers and tools to measure the poses of patients and instruments. The measuring systems are calibrated previously for a disturbance free environment. Ferromagnetic material near the field generator changes the electromagnetis field and thus influences the position detection of the sensor coils.

[0062] The disturbance of the measuring system caused by the microscope and/or by a shielding has to be optimally compensated in order to allow a correct position measurement of the patient and the used navigated instruments.

[0063] One possible implementation is “distortion mapping correction”. With that, a correction for the position and orientation of the sensor is calculated based on a previous calibration for each position in the measurement field. The position and orientation of the sensor coil can be described as a translation (X, Y, Z) and orientation in the form of Euler angles (Ψ, Θ, Φ). The correction can be also be dependent of the current microscope settings (microscope parameter vector m) and the current setting of the field generator mounting adjustment element (parameter vector f). Hence the correction function yields for the calculation of the corrected pose vector p.sub.c based on the input parameters q=(x, y, z, Ψ, Θ, Φ, m, f):

[00001]$p_c=\left(\begin{array}{c}{x}_c\\ y_c\\ z_c\\ {\Psi }_c\\ {\Theta }_c\\ {\Phi }_c\end{array}\right)=g\left(q\right)=g\left(\begin{array}{c}x\\ y\\ z\\ \Psi \\ \Theta \\ \Phi \\ m\\ f\end{array}\right)$

[0064] Possible implementations of the correction function g can be based on polynomials or splines. With polynomials the corrected output values p.sub.c=(x.sub.c, y.sub.c, z.sub.c, Ψ.sub.c, Θ.sub.c, Φ.sub.c).sup.T based on the input parameters q=(x, y, z, Ψ, Θ, Φ, m, f) with the single values q.sub.i and 1<=i<=n are determined as follows:

[00002]$p_c=\left(\begin{array}{c}{x}_c\\ y_c\\ z_c\\ {\Psi }_c\\ {\Theta }_c\\ {\Phi }_c\end{array}\right)=A\left(\begin{array}{c}1\\ q_1^1\\ q_1^2\\ \mathrm{.Math.}\\ q_1^k\\ q_2^1\\ q_2^2\\ \mathrm{.Math.}\\ q_2^k\\ \mathrm{.Math.}\\ \mathrm{.Math.}\\ q_n^1\\ q_n^2\\ \mathrm{.Math.}\\ q_n^k\end{array}\right)$

[0065] wherein k indicates the degree of the polynomials and A indicates a 6×(n.Math.k+1) matrix which contains the coefficients of the polygons that are determined during an initial calibration.

[0066] By using a known shielding, the influence on the electromagnetic field can be calculated using the finite difference method or the finite element method. In particular, the change of direction and strength of the field in the measurement space of the electromagnetic measuring system can be quantitatively predicted. This allows in large parts to compensate the influence of the electromagnetic field caused by the shielding.

[0067] The data acquisition unit captures, digitizes and if necessary temporarily stores the data, which is continuously arriving from the microscope image data stream, and the communicated microscope settings for zoom and focus. Furthermore, the position and orientation data of the sensor coils are cached, detected by the electromagnetic measuring system, and made available to the data processing module.

[0068] The data storage unit stores the three-dimensional image data of the patient and, if necessary the calibration data of the disturbance correction module of the electromagnetic measuring system and of the microscope registration module. These data are made available when needed for the data processing unit.

[0069] The data processing unit has the task to combine navigation data from the electromagnetic measuring system, the 3D image data and calibration data from the data storage unit and the microscope images from the surgical microscope, in order to calculate useful views and images for the user. They may include: [0070] Slice images of the 3-D image data at the position of the tool center point of a navigated instrument or the focal point of the microscope [0071] Perspective or orthographic 3-D view of the image data of the patients with illustrated position of the tracked instruments and/or the microscope [0072] Microscope image view with positionally correct superposition of planning data based on the pre-operative 3-D image data and the navigation data [0073] Virtual microscope image with planning data for injecting in the microscope optic.

[0074] The following sub-modules may be part of the data processing unit:

[0075] The image data registration module has the task of determining continuously the spatial relationship between the field generator of the electromagnetic measuring system and the 3D image data set. For this purpose, an electromagnetic sensor is usually attached to the patient near the operating field in order to serve as a reference system for the position of the 3D image data. The pose of this electromagnetic sensor is continuously detected by the electromagnetic measuring system. Methods for the intraoperative determination of the rigid transformation between the reference coordinate systems of the 3D image data and of the patient sensor are well-known in state of the art, such as landmarks-based and surface-based methods (Eggers, Mühling & Marmulla, International Journal of Oral and Maxillofacial Surgery, 2006, 35(12), 1081-1095.; Simon, Hebert & Kanade, International Journal of Oral and Maxillofacial Surgery, 1995, 35(12), 1081-1095), which can be used in this module.

[0076] The microscope registration module calculates and continuously updates the imaging properties of the microscope as a function of the current microscope settings (e.g. zoom and focus) and, if applicable, of the setting of the adjustment element of the field generator. When modeling the microscope as a pinhole camera, the intrinsic and extrinsic camera parameters for the current zoom and focus setting of the microscope can be determined based on a previous calibration. The intrinsic parameters may include the focal length, the image center and the aspect ratio and parameters for the description of non-linear distortion. The extrinsic camera parameters include the translational and rotational parameters of the rigid transformation between the reference coordinate system of the electromagnetic measuring system and the origin of the pinhole camera model.

[0077] The computation of the camera parameters can be calculated similarly to the disturbance correction module using polynomials or splines based on the current zoom and focus settings of the microscope or on the setting of the adjustment element. Relevant prior art in this field of microscope registration is (Edwards et al., IEEE Transactions on Medical Imaging, 2000, 19(11), 1082-1093; Garcia Girladez et al., International Journal of Computer Assisted Radiology and Surgery, 2007, 1(5), 253-264; Holloway, 1995, University of North Carolina at Chapel Hill, Chapel Hill, N.C., USA). The microscope registration is computed automatically during surgery, a support by the user is not necessary.

[0078] The image computation module calculates views and image data for the presentation on the image display unit or for the injection in the microscope optic. Here, the current output data of the image data registration module, of the microscope registration module and of the data acquisition unit are used, in particular the current transformation between the electromagnetic measuring system and 3D image data and other navigated instruments, the current transformation between the electromagnetic measuring system and the origin of the camera system in accordance with the pinhole camera model and the intrinsic camera parameters.

[0079] These transformations allow transferring the patient planning data marked in the 3D image data into the reference coordinate system of the microscope camera. Then, the current intrinsic camera parameters are used to calculate the mapping of the planning data onto the image plane of the microscope. This enables the computation of the virtual microscope images. For the superimposed microscope image views, the real and virtual microscope image data are combined and shown on the image display unit.

[0080] In addition, these transformations also allow the calculation of slice images of the 3D image data through the position of the tool center point of the navigated instrument or through the focal point of the microscope.

[0081] The image display unit is used to display the generated views and image data on a screen.

[0082] The optional shielding is made of a ferromagnetic material, which disturbs the electromagnetic field of the electromagnetic measuring system, and thus overlays the disturbance caused the microscope or other metal objects. The knowledge of the disturbance of the electromagnetic field by the shielding is gained during a simulation and/or a calibration. So, the influencing of the navigation data of the measuring system can be eliminated or at least substantially reduced due to the shielding.

[0083] The shielding can preferably have the following properties: [0084] The shield can consists of ferromagnetic material, in particular aluminum. [0085] The shielding is mounted between the microscope and field generator. [0086] The shielding is flat, or consists of one or more flat plates, in order to achieve a sufficient disturbance overlay in particular of the microscope. [0087] The shielding may have an opening at the position of the microscope lens in order not to interrupt the view of the microscope on the operation field.

[0088] The following system modifications can be of advantage:

[0089] Sensor coils can be mounted or installed rigidly to the field generators. During surgery, the pose of the electromagnetic sensors can be continuously monitored and checked for changes. Firstly, this helps to determine whether at least one field generator, the microscope or the shielding are not in the expected configuration. Secondly, a temporary disturbance of the electromagnetic field caused by an unexpected adjustment of zoom and focus of the microscope by electric motors can be detected. The detection of these disturbances allows the warning of the user and the prevention of the display of incorrect position information.

[0090] Another modification is to have a dynamically adjustable position and orientation of the field generator under the microscope. The following benefits are expected: [0091] Optimization of the average volume of the viewing area of the microscope and the working space of the electromagnetic measuring system [0092] Automatic optimal alignment of the electromagnetic measuring system, both on the field of view of the microscope and on the position of the patient reference sensor, which can be mounted distantly.

[0093] The improved integration of the electromagnetic measuring system is realized by a rigid, possibly reproducible mounting of the field generator at the microscope, particularly at the bottom of the microscope. This allows an initial calibration of the pose and of the imaging characteristics of the microscope optical system relative to a reference coordinate system of the electromagnetic measuring system. For a correct overlay of planning data in the microscope image no intraoperative calibration will be necessary.

[0094] To compensate the disturbance which is expected to be caused by the metal of the surgical microscope, a disturbance correction module is introduced which eliminates or reduced the influencing of the surgical microscope based on a one-time-only calibration of the changes of the electromagnetic field. To minimize the disturbance, which is caused by the metal of the surgical microscope, a shielding can be mounted between the field generator and the microscope. In that case, the shielding overlays the disturbance of the microscope and minimizes the effects of the microscope disturbances on the pose measurement.

[0095] The advantages of the invention are: [0096] usability of electromagnetic navigation for microscopic surgery [0097] No time-consuming alignment of the field generator to the operation area as the surgeon performs the alignment implicitly by positioning the microscope [0098] No intraoperative calibration is necessary as the position and orientation of the field generator is known relative to the microscope optics

DETAILED DESCRIPTION OF THE FIGURES

[0099] FIG. 1 shows a system structure with an operating microscope, the electromagnetic (EM) measurement system consisting of the field generator and the EM sensors, which are integrated into the navigated instruments and the patient tracker. The field generator is mounted below the microscope and creates an electromagnetic field for measuring the position of EM sensors with integrated sensor coils underneath the microscope.

[0100] Between the microscope and the field generator is a shield in the form of a plate, particularly made of ferromagnetic material. The field generator and the EM sensors in the navigated instruments and the patient trackers are connected via cables to the EM-measuring system. During surgery, the microscope is positioned over the surgical field where the patient is positioned generally on the operating table. The surgeon sees the highly magnified stereoscopic view of the operating field through the eyepieces of the microscope.

[0101] FIG. 2 discloses an embodiment, wherein the field generator is fixed mounted to the microscope together with a shield. The field generator is constructed with an opening in its centre, so that an uninterrupted view of the microscope through the microscope lens on the operating field is possible. The shield has a corresponding circular opening, if necessary an additional annular shield around this opening must be attached. The shape of the field generator is approximately circular, but the shape is optimized for the installation of elongated coils. Alternative forms such a torus or other solid of revolutions are also conceivable.

[0102] The size and shape of the field generator is configured such that the measuring range of the electromagnetic measurement system covers at least the sharply displayable field of view of the microscope.

[0103] FIG. 3 shows a further possible embodiment of the field generator and its attachment to the microscope. Here, the field generator is approximately cuboid and is mounted below the microscope beside the microscope lens. With the aid of an adjusting element, the orientation of the field generator can be changed manually or automatically towards the microscope lens so that the measurement range of the electromagnetic measurement system include as much as possible of the field of view of the microscope.

[0104] The adjusting element is realized as in this embodiment as a linear actuator in combination with a rotational joint. Alternative implementations of the mounting of the field generator on the microscope can be realised with rotational or spherical joints, which are driven pneumatically or hydraulically if necessary. The adjustment element also comprises a sensor element to detect the state of the adjustment element and to enable to deduce the current position of the field generator relative to the microscope. Further, a shield is mounted between the microscope and the field generator, which has an opening for the microscope lens.

[0105] FIG. 4 shows the same embodiment as depicted in FIG. 3. In addition, the field of view of the microscope and the measuring range of the electromagnetic measurement system are shown in the hatched areas. It is obvious that the orientation of the field generator under the microscope is crucial for achieving an overlap of the microscopic field of view and the measurement range of the electromagnetic measurement system. The overlapping area is necessary for the pose measurement of EM sensors or navigated instruments, which are visible in the microscope image. An additional requirement arising from the need for continuous measurement of the pose of the patient tracker is to locate the patient tracker in the measurement region of the electromagnetic measuring system. To ensure this, the orientation of the field generator can be changed intra-operatively manually or automatically, if necessary. Optimising the orientation of the field generator so that the patient tracker and the navigated instruments are located in the optimum measurement region of the electromagnetic measurement system can also increase the accuracy of the position measurement.

[0106] FIG. 5 discloses the data flow between the system components and subcomponents for the system configuration with an operating microscope, which supports image injection. The main components include the surgical microscope, the electromagnetic measurement system, the adjustment element, the data acquisition unit, the data storage unit, the data processing unit and the image display unit.

[0107] The microscope provides a continuous data stream of the current microscope image data using a digital or analogue video interface. This video data stream as well as a separate data stream with the current microscope settings, such as zoom and focus is transferred to the data acquisition unit. Additionally, the electromagnetic measurement system transmits the navigation data as well as the adjustment element its state to the data acquisition unit.

[0108] The data acquisition unit receives the microscope settings data and the adjustment element state. Those data are transmitted to the disturbance correction module in order to perform a correction of the navigation data dependent on the current microscope settings and mounting of the field generator on the microscope. The data acquisition unit provides the data processing module with all current data of the microscope and the measurement system. In addition, the data processing unit can access the 3D image data of the patient and calibration data via the data storage unit. The subcomponents image data registration modules, microscope registration module and the image computation module process this data. The image computation module calculates image data for display on the image display unit as well as for injecting in the microscope optics.

REFERENCE NUMBER LIST

[0109] 1Microscope [0110] 3 Adjustment Element [0111] 5 Microscope Lens [0112] 8 Microscopic Field of View [0113] 10 Eyepiece [0114] 15 Shielding [0115] 18 Field Generator [0116] 20 Electromagnetic Measurement System [0117] 22 Electromagnetic Measurement Region [0118] 25 Pointer with sensor elements [0119] 30 Patient Tracker with sensor elements [0120] 50 Operating Table [0121] 100 Patient